1893. THE GENESIS OF MOUNTAIN RANGES. 373 



an assumption afterwards proved incorrect in several important 

 particulars. It is impossible to state any theory without involving 

 cause and effect, and what is not observation in these theories is 

 mostly physics. 



After explaining the contraction theory, Professor Le Conte gives 

 a summary of the objections to it, and a formidable list it is — too 

 extensive, indeed, to enumerate in the space I limit myself to. Many 

 of these difficulties have been dealt with in my " Origin of Mountain 

 Ranges," especially the most salient of them, based on the existence of a 

 level-of-no-strain at no great depth in the crust of the globe, above which 

 the crust is in compression and below in tension. Le Conte evidently 

 attaches great importance to this principle, and he may well do so, as 

 it clearly follows that the bulk of the crust in compression is quite 

 inadequate to account for the irregularities of the earth's surface. 



Reade's Expansion Theories are next dealt with, and Professor Le 

 Conte honours me with a generally fair formal statement of my views. 

 He feels, however, that he does not thoroughly grasp my meaning in 

 several important particulars, more especially in relation to the cumu- 

 lative effects of recurrent expansion. It would savour of self-conceit 

 to repeat my views here, indeed it is unnecessary, as the theories 

 and investigations can be perused in their original extended form, by 

 which a more just conception of their value, whatever that may 

 eventually prove to be, can be formed. 



After stating the objections to Reade's theories, which will be 

 dealt with further on, Duttons Isostatic Theory and Reyer's Gliding Theory 

 are explained and dismissed — Le Conte finally, whether we may agree 

 with him in whole, or part, or entirely dissent, concludes a very able 

 address, written in the clear and charming style peculiar to himself, 

 with the following sentence: " After this rapid discussion of alternative 

 theories, in which we have found them all untenable, we return again 

 to the contraction theory, not, indeed, with our old confidence, but 

 with the conviction that it is even yet the best working hypothesis 

 we have." 



Before criticising the theories of this able investigator and writer, 

 many of which are quite individual and original, I think it will be 

 best to dwell first upon those general principles in which we are in 

 agreement. They are these : (i) The leading principle, and one first 

 stated in America by Professor James Hall, is that mountain ranges 

 are built up out of immense thicknesses of sediment ; (2) that there 

 is a relation of cause and effect between sedimentation and mountain 

 building which Le Conte attempts to explain in one way consistent 

 with the Contraction Theory, and I in another in more direct relation 

 to my Expansion Theory. This is a very important agreement, as 

 there are still some, though in a minority, who are not prepared to 

 admit either the fact or the relation. It is nearly seven years since I 

 published my work, and the additions to our knowledge, too numerous 

 to mention here, all point to the fact that Mountain Ranges are built 



